Zoom optical system, optical apparatus and method of manufacturing zoom optical system

ABSTRACT

A zoom optical system includes, in order from its object side along its optical axis, a first lens group G 1  having a positive refracting power, a second lens group G 2  having a negative refracting power, a third lens group G 3  having a positive refracting power, and a fourth lens group G 4  having a positive refracting power, wherein at least one of the first, second, third and fourth lens groups G 1 , G 2 , G 3 , G 4  comprises a front group having a positive refracting power including at least two lenses and a rear group having a negative refracting power, and during zooming from the wide angle end state W to the telephoto end state T, the distance between the front group and the rear group does not change, and during focusing onto an object, the front group moves along the optical axis.

The disclosure of the following priority application is hereinincorporated by reference:

Japanese Patent Application No. 2010-063123 filed on Mar. 18, 2010.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a zoom optical system, an opticalapparatus having the same, and a method of manufacturing a zoom opticalsystem.

2. Background Art

Heretofore, zoom optical systems suitable for use in film cameras,digital still cameras, and video cameras have been developed (see, forexample, Japanese Patent Application Laid-Open No. 2006-201524).

Prior art zoom optical systems have not achieved excellent opticalperformance.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and its objectis to provide a zoom optical system having excellent optical performanceand an optical device having such a zoom optical system, and a method ofmanufacturing a zoom optical system.

To achieve the above object, according to the present invention, thereis provided a zoom optical system comprising, in order from its objectside along its optical axis a first lens group having a positiverefracting power, a second lens group having a negative refractingpower, a third lens group having a positive refracting power, and afourth lens group having a positive refracting power, wherein at leastone of said first, second, third and fourth lens groups comprises afront group having a positive refracting power including at least twolenses and a rear group having a negative refracting power, the distancebetween said front group and said rear group does not change duringzooming from the wide angle end state to the telephoto end state, andsaid front lens group moves along the optical axis during focusing ontoan object.

According to another aspect of the present invention, there is providedan optical apparatus having said zoom optical system.

According to still another aspect of the present invention, there isprovided a method of manufacturing a zoom optical system including, inorder from its object side along its optical axis, a first lens grouphaving a positive refracting power, a second lens group having anegative refracting power, a third lens group having a positiverefracting power and a fourth lens group having a positive refractingpower. The method according to the present invention includesconstructing at least one of said first, second, third and fourth lensgroups with a front group having a positive refracting power includingat least two lenses and a rear group having a negative refracting power,arranging said front group and said rear group in such a way that thedistance between said front group and said rear group will not changeduring zooming from the wide angle end state to the telephoto end state,and arranging said front group in such a way as to be movable along theoptical axis upon focusing onto an object.

The present invention can provide a zoom optical system having goodoptical performance, an optical apparatus having the same, and a methodof manufacturing a zoom optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing the configuration of a zoomoptical system according to a first example.

FIGS. 2A, 2B and 2C are aberration diagrams of the zoom optical systemaccording to the first example in the state in which the zoom opticalsystem is focused on an object point at infinity, where FIG. 2A showsaberrations at the wide angle end of the focal length range, FIG. 2Bshows aberrations at an intermediate focal length position, and FIG. 2Cshows aberrations at the telephoto end of the focal length range.

FIGS. 3A and 3B show aberrations of the zoom optical system according tothe first example in the state in which the optical system is focused onan object point at a short distance, where FIG. 3A shows aberrations atthe wide angle end of the focal length range, and FIG. 3B showsaberrations at the telephoto end of the focal length range.

FIG. 4 is a cross sectional view showing the configuration of a zoomoptical system according to a second example.

FIGS. 5A, 5B and 5C are aberration diagrams of the zoom optical systemaccording to the second example in the state in which the zoom opticalsystem is focused on an object point at infinity, where FIG. 5A showsaberrations at the wide angle end of the focal length range, FIG. 5Bshows aberrations at an intermediate focal length position, and FIG. 5Cshows aberrations at the telephoto end of the focal length range.

FIGS. 6A and 6B show aberrations of the zoom optical system according tothe second example in the state in which the optical system is focusedon an object point at a short distance, where FIG. 6A shows aberrationsat the wide angle end of the focal length range, and FIG. 6B showsaberrations at the telephoto end of the focal length range.

FIG. 7 is a cross sectional view showing the configuration of a zoomoptical system according to a third example.

FIGS. 8A, 8B and 8C are aberration diagrams of the zoom optical systemaccording to the third example in the state in which the zoom opticalsystem is focused on an object point at infinity, where FIG. 8A showsaberrations at the wide angle end of the focal length range, FIG. 8Bshows aberrations at an intermediate focal length position, and FIG. 8Cshows aberrations at the telephoto end of the focal length range.

FIGS. 9A and 9B show aberrations of the zoom optical system according tothe third example in the state in which the optical system is focused onan object point at a short distance, where FIG. 9A shows aberrations atthe wide angle end of the focal length range, and FIG. 9B showsaberrations at the telephoto end of the focal length range.

FIG. 10 is a cross sectional view showing the configuration of a zoomoptical system according to a fourth example.

FIGS. 11A, 11B and 11C are aberration diagrams of the zoom opticalsystem according to the fourth example in the state in which the zoomoptical system is focused on an object point at infinity, where FIG. 11Ashows aberrations at the wide angle end of the focal length range, FIG.11B shows aberrations at an intermediate focal length position, and FIG.11C shows aberrations at the telephoto end of the focal length range.

FIGS. 12A and 12B show aberrations of the zoom optical system accordingto the fourth example in the state in which the optical system isfocused on an object point at a short distance, where FIG. 12A showsaberrations at the wide angle end of the focal length range, and FIG.12B shows aberrations at the telephoto end of the focal length range.

FIG. 13 is a cross sectional view schematically showing the constructionof a camera equipped with the zoom optical system according to the firstexample.

FIG. 14 is a flow chart of a method of manufacturing a zoom opticalsystem according to the present invention.

DETAILED DESCRIPTION

In the following, a zoom optical system according to an embodiment ofthe present invention will be described.

A zoom optical system according to an embodiment of the inventioncomprises, in order from its object side along its optical axis, a firstlens group having a positive refracting power, a second lens grouphaving a negative refracting power, a third lens group having a positiverefracting power, and a fourth lens group having a positive refractingpower, wherein at least one of the first, second, third and fourth lensgroups comprises a front group having a positive refracting powerincluding at least two lenses and a rear group having a negativerefracting power, and during zooming from the wide angle end state tothe telephoto end state, the distance between the front group and therear group does not change, and during focusing onto an object, thefront lens group moves along the optical axis.

With the above configuration, the amount of movement of the focusinggroup upon focusing can be made small. This enables a reduction in theload on the motor and a reduction in the overall optical length.Furthermore, the focusing group can be designed to have an adequatepower arrangement without imposing undue burden of power to the entireoptical system, and deterioration of the optical performance caused bymanufacturing errors can be made smaller. Still further, the change inspherical aberration of the optical system in the telephoto end statecan be made small, and excellent optical performance can be achievedeven when the optical system is focused on an object at a shortdistance. Still further, since the distance between the front group andthe rear group does not change during zooming, the change in thedecentering of the front group and the rear group relative to each othercan be made small. This makes deterioration of the optical performancedue to manufacturing errors smaller.

In the zoom optical system according to this embodiment, it is preferredthat the first lens group be fixed relative to the image plane duringzooming from the wide angle end state to the telephoto end state.

This design can make the change in the decentering of the first lensgroup made small, thereby making deterioration of the opticalperformance due to manufacturing errors smaller. As the first lens groupis not moved during zooming, the overall size of the zoom optical systemcan be made small.

It is preferred that the zoom optical system according to thisembodiment satisfy the following condition (1):

0.050<|fA/fB|<0.950  (1),

where fA is the focal length of the front group, and fB is the focallength of the rear group.

Condition (1) limits the value of the ratio of the focal length of thefront group and the focal length of the rear group.

If condition (1) is satisfied, the amount of movement of the front groupfor focusing can be made small, and excellent correction of the changein aberrations, in particular spherical aberration, at short objectdistances can be achieved.

If the upper limit of condition (1) is exceeded, the amount of movementof the front group for focusing will be unduly large, leading to a largeoverall length of the optical system. This is undesirable. In addition,undercorrection of spherical aberration will result.

If the lower limit of condition (1) is exceeded, the refracting power ofthe front group will be unduly high, leading to overcorrection ofspherical aberration. In addition, deterioration in the opticalperformance due to decentering of the front group and rear grouprelative to each other will be large when the optical system is focusedon an object at a short distance. This is undesirable.

To ensure the advantageous effects of this embodiment, it is preferredthat the upper limit of condition (1) be replaced by 0.700. To furtherensure the advantageous effects of this embodiment, it is more preferredthat the upper limit of condition (1) be replaced by 0.400. To ensurethe advantageous effects of this embodiment still further, it is morepreferred that the upper limit of condition (1) be replaced by 0.250.

To ensure the advantageous effects of this embodiment, it is preferredthat the lower limit of condition (1) be replaced by 0.070. To furtherensure the advantageous effects of this embodiment, it is more preferredthat the lower limit of condition (1) be replaced by 0.130. To ensurethe advantageous effects of this embodiment still further, it is morepreferred that the lower limit of condition (1) be replaced by 0.170.

In the zoom optical system according to this embodiment, it is preferredthat the lens group located closest to the image side be fixed relativeto the image plane during zooming from the wide angle end state to thetelephoto end state.

This feature allows a simplification of the zoom mechanism for theentire optical system. In addition, this feature facilitates keeping theF-number constant during zooming and is advantageous for aberrationcorrection.

In the zoom optical system according to this embodiment, it is preferredthat at least a part of the fourth lens group be movable with a movementcomponent in a direction perpendicular to the optical axis.

This feature allows a simplification and a weight reduction of avibration reduction mechanism for compensating hand shake.

It is preferred that the zoom optical system according to thisembodiment satisfy the following condition (2):

0.050<|fA/fX|<0.950  (2),

where fA is the focal length of the front group, and fX is the focallength of the above-mentioned at least one lens group.

Condition (2) limits the ratio of the focal length of the front groupand the above-mentioned at least one lens group.

If condition (2) is satisfied, the amount of movement of the front groupfor focusing can be made small, and aberrations, in particular thechange in spherical aberration, can be corrected excellently when theoptical system is focused at an object at a short distance.

If the upper limit of condition (2) is exceeded, the amount of movementof the front group for focusing will be unduly large, leading to anundesirably large overall length of the zoom optical system. Inaddition, undercorrection of spherical aberration will result.

If the lower limit of condition (2) is exceeded, the refracting power ofthe front group will be unduly high, leading to overcorrection ofspherical aberration. In addition, a deterioration in the opticalperformance caused by decentering of the front group and the rear grouprelative to each other will become large when the optical system isfocused at an object at a short distance. This is undesirable.

To ensure the advantageous effects of this embodiment, it is preferredthat the upper limit of condition (2) be replaced by 0.920. To furtherensure the advantageous effects of this embodiment, it is more preferredthat the upper limit of condition (2) be replaced by 0.880. To ensurethe advantageous effects of this embodiment still further, it is morepreferred that the upper limit of condition (2) be replaced by 0.850.

To ensure the advantageous effects of this embodiment, it is preferredthat the lower limit of condition (2) be replaced by 0.200. To furtherensure the advantageous effects of this embodiment, it is more preferredthat the lower limit of condition (2) be replaced by 0.500. To ensurethe advantageous effects of this embodiment still further, it is morepreferred that the lower limit of condition (2) be replaced by 0.800.

It is preferred that the zoom optical system according to thisembodiment satisfy the following condition (3):

1.200<|fB/fX|<50.000  (3),

where fB is the focal length of the rear group, and fX is the focallength of the above-mentioned at least one lens group.

Condition (3) limits the ratio of the focal length of the rear group andthe above-mentioned at least one lens group.

If condition (3) is satisfied, the overall length of the optical systemcan made small, and aberrations, in particular the change in sphericalaberration, can be corrected excellently when the optical system isfocused at an object at a short distance.

If the upper limit of condition (3) is exceeded, the refracting power ofthe front group will be unduly high, leading to overcorrection ofspherical aberration. In addition, a deterioration in the opticalperformance caused by decentering of the front group and the rear grouprelative to each other will become large when the optical system isfocused at an object at a short distance. This is undesirable.

If the lower limit of condition (3) is exceeded, the amount of movementof the front group for focusing will be unduly large, leading to anundesirably large overall length of the zoom optical system. Inaddition, undercorrection of spherical aberration will result.

To ensure the advantageous effects of this embodiment, it is preferredthat the upper limit of condition (3) be replaced by 25.000. To furtherensure the advantageous effects of this embodiment, it is more preferredthat the upper limit of condition (3) be replaced by 10.000. To ensurethe advantageous effects of this embodiment still further, it is morepreferred that the upper limit of condition (3) be replaced by 5.000.

To ensure the advantageous effects of this embodiment, it is preferredthat the lower limit of condition (3) be replaced by 1.500. To furtherensure the advantageous effects of this embodiment, it is more preferredthat the lower limit of condition (3) be replaced by 2.500. To ensurethe advantageous effects of this embodiment still further, it is morepreferred that the lower limit of condition (3) be replaced by 3.500.

In the zoom optical system according to this embodiment, the lens groupcomposed of the front group and the rear group be the third lens group.

If this is the case, the outer diameter of the focusing group can bemade small, and a reduction in the weight can be achieved. In addition,good optical performance can be achieved even when the optical system isfocused on an object at a short distance.

In the zoom optical system according to this embodiment, the lens groupcomposed of the front group and the rear group be the first lens group.

If this is the case, the change in the focal length with focusingoperation can be made small, and the imaging magnification of an objectat short distance can be made large.

In the zoom optical system according to this embodiment, it is preferredthat the front group include at least one positive lens and at least onenegative lens.

With this feature, curvature of field, spherical aberration andchromatic aberration at the time when the optical system is focused onan object at a short distance can be made small. Therefore, good opticalperformance can be achieved even at the time when the optical system isfocused on an object at a short distance.

In the zoom optical system according to this embodiment, it is preferredthat during zooming from the wide angle end state to the telephoto endstate, the distance between the first lens group and the second lensgroup increase, the distance between the second lens group and the thirdlens group change, and the distance between the third lens group and thefourth lens group change.

With this feature, the change in spherical aberration can be made small.

In the following, examples according to the aforementioned embodimentwill be described with reference to the drawings.

First Example

FIG. 1 is a cross sectional view showing the configuration of a zoomoptical system according to a first example.

As shown in FIG. 1, the zoom optical system according to the firstexample includes, in order from its object side along its optical axis,a first lens group G1 having a positive refracting power, a second lensgroup G2 having a negative refracting power, a third lens group G3having a positive refracting power, and a fourth lens group G4 having apositive refracting power. The third lens group G3 is composed of afront group G3A having a positive refracting power and a rear group G3Bhaving a negative refracting power. An aperture stop S is provided inthe fourth lens group G4, and the aperture stop S is the element that islocated closest to the object side in the fourth lens group G4.

During zooming from the wide angle end state W to the telephoto endstate T, the first lens group G1 is fixed, the second lens group G2moves monotonically toward the image side, the third lens group G3moves, and the fourth lens group G4 is fixed, relative to the imageplane I so that the distance between the first lens group G1 and thesecond lens group G2 increases, that the distance between the secondlens group G2 and the third lens group G3 changes, and that the distancebetween the third lens group G3 and the fourth lens group G4 changes. Inaddition, during zooming from the wide angle end state W to thetelephoto end state T, the distance between the front group G3A in thethird lens group G3 and the rear group G3B in the third lens group G3does not change.

Focusing operation from an object at infinity to an object at a shortdistance is performed by moving the front group G3A in the third lensgroup G3 toward the image side along the optical axis.

The first lens group G1 includes, in order from the object side alongthe optical axis, a cemented lens made up of a negative meniscus lensL11 having a convex surface facing the object side and a biconvex lensL12, and a positive meniscus lens L13 having a convex surface facing theobject side.

The second lens group G2 includes, in order from the object side alongthe optical axis, a negative meniscus lens L21 having a convex surfacefacing the object side, a cemented lens made up of a biconcave lens L22and a biconvex lens L23, and a biconcave lens L24.

The front group G3A in the third lens group G3 includes, in order fromthe object side along the optical axis, a biconvex lens L31, and acemented lens made up of a negative meniscus lens L32 having a convexsurface facing the object side and a biconvex lens L33.

The rear group G3B in the third lens group G3 includes a negativemeniscus lens L34 having a concave surface facing the object side.

The fourth lens group G4 includes, in order from the object side alongthe optical axis, a biconvex lens L41, a cemented lens made up of abiconvex lens L42 and a biconcave lens L43, a fixed stop FS, a cementedlens made up of a biconvex lens L44 and a biconcave lens L45, abiconcave lens L46, a biconvex lens L47, a biconvex lens L48, and anegative meniscus lens L49 having a concave surface facing the objectside. The rays emerging from the negative meniscus lens L49 are focusedon the image plane I.

The image plane I is arranged on an image pickup element (not shown),which may be, for example, a CCD or CMOS sensor. This applies also toall the examples described in the following.

Hand-shake compensation (or vibration reduction) is provided by moving aportion of the fourth lens group G4 or the cemented lens made up of thebiconvex lens L44 and the biconcave lens L45 and the biconcave lens L46in such a way as to have a movement component in a directionperpendicular to the optical axis.

Numerical data for the zoom optical system according to the firstexample is presented in Table 1 below.

In the surface data in the table, “OP” refers to the object plane, “SN”stands for “surface number” representing the ordinal position of a lenssurface counted from the object side, “r” is the radius of curvature,“d” is the surface distance, “nd” is the refractive index with respectto the d-line (having a wavelength λ of 587.6 nm), “νd” is the Abbenumber with respect to the d-line (having a wavelength λ of 587.6), “OS”refers to the object surface, “variable” refers to a variable surfacedistance, “stop” refers to an aperture stop S, and “IP” refers to theimage plane I. The refractive index nd of air (which is equal to1.000000) is not shown. The sign “∞” in the radius of curvature rrepresents that the corresponding surface is a flat surface.

In the “Aspheric Surface Data” section, aspheric surfaces arerepresented by the following equation:

X(y)=(y ² /r)/[1+[1−k(y ² /r ²)]^(1/2) ]+A4×y ⁴ +A6×y ⁶

where y is the height from the optical axis in directions perpendicularto the optical axis, X(y) is the displacement in the optical axisdirection at height y (or the distance between the tangential plane ofeach aspheric surface at its vertex and a point on the aspheric surfacealong the optical axis), r is the radius of curvature of a base sphere(or the paraxial radius of curvature), k is the conic constant, and Anis the n-th order aspheric coefficient. The expression “E-n” stands for“×10^(−n)”, for example, “1.234E-05” stands for “1.234×10⁻⁵”. Asphericsurfaces are marked by asterisk “*” suffixed to there surface numbers inthe surface data.

In the “Various Data” section, the zoom ratio refers to themagnification changing ratio of the zoom optical system, “W” stands forthe wide angle end state, “M” stands for an intermediate focal lengthstate, “T” stands for the telephoto end state, “f” is the focal lengthof the entire lens system, “FNO” is the F-number, “ω” is half the angleof view (in degrees), “Y” is the image height, “TL” is the overalllength of the lens system or the distance from the surface closest tothe object side in the first lens group G1 to the image plane I in thestate in which the lens system is focused at an object at infinity, “Bf”is the back focus, and “di” is the value of the variable surfacedistance for the surface with surface number i.

In the “Data for Short Object Distance” section, “W” stands for the wideangle end state, “M” stands for an intermediate focal length state, “T”stands for the telephoto end state, “β” is the image magnification inthe state in which the lens system is focused on an object at a shortdistance, “d0” is the distance from the object to the lens surfaceclosest to the object side, and “di” is the value of the variablesurface distance for the surface with surface number i.

In the “Data of Zoom Lens Group” section, the surface number of thefirst (or frontmost) lens surface (FLS) in each lens group and the focallength (FL) of each lens group are presented.

In the “Values Associated with Conditions” section, values associatedwith conditions are presented.

In all the numerical data presented in the following, the values of thefocal length f, the radius of curvature r, the surface distance andother lengths are in millimeters, unless stated otherwise. However,since scaled-up and scaled-down optical systems can also achieve similaroptical performance, the dimensions are not limited to those presentedin the following. The unit of the values is not limited to millimeters,but other appropriate units may be used. The above description of thesymbols also applies to the other example that will be described in thefollowing.

TABLE 1 (Surface Data) SN r d nd νd OP ∞ ∞  1 107.5999 2.5000 1.83337833.17  2 62.4829 8.8000 1.497820 82.52  3 −3786.7547 0.1000  4 62.19208.5000 1.497820 82.52  5 2842.4167 (variable)  6 2570.3752 2.00001.824372 41.37  7 33.8242 5.9498  8 −74.3443 1.8000 1.488625 71.58  936.7151 4.7771 1.846660 23.78 10 −780.6979 2.6316 11 −49.1692 1.80001.729157 54.66 12 487.4476 (variable) 13 133.3716 3.4283 1.729157 54.6614 −119.7323 0.1000 15 146.3097 2.0000 1.834000 37.16 16 42.6439 5.90001.603001 65.46 17 −89.8556 (variable) 18 −50.0000 2.0000 1.761705 29.1919 −69.7595 (variable) 20 (stop) ∞ 0.0000 21 52.0128 3.7289 1.71644555.44 22 −358.6198 0.1000 23 44.5918 4.0000 1.497820 82.52 24 −375.05812.0000 1.849814 30.97 25 50.7950 18.7122  26 ∞ 2.0000 27 69.5944 3.40001.808090 22.79 28 −100.4799 1.6000 1.657677 54.98 29 34.2068 2.6410 30−346.1430 1.6000 1.841009 30.09 31 70.2413 3.0000 32 55.6811 3.90001.514739 64.49 33 −95.4983 0.1000 34 59.3918 3.9000 1.514062 64.62 35−131.7941 4.9899 36 −37.0818 1.9000 1.800999 34.96 37 −73.3082 (Bf) IP ∞W M T (Various Data) zoom ratio: 2.745 f = 71.40 107.00 195.99 FNO = 4.14.1 4.1 ω = 17.107 11.288 6.107 Y = 21.6 21.5 21.6 TL = 214.6 214.5214.8 Bf = 51.9 51.8 52.1 d5 1.500 20.365 37.947 d12 19.359 14.159 0.800d17 13.065 13.065 13.065 d19 18.897 5.232 0.800 (Data for Short ObjectDistance) β −0.07 −0.09 −0.14 d0 974.91 975.02 974.94 d5 1.500 20.36537.947 d12 21.152 17.825 11.097 d17 11.272 9.398 2.778 d19 18.897 5.2320.800 (Data of Zoom Lens Group) Group FLS FL 1 1 98.012 2 6 −25.197 3 1366.600 3A 13 55.298 3B 18 −242.351 4 20 97.939 (Values Associated withConditions) (1) |fA/fB| = 0.228 (2) |fA/fX| = 0.830 (3) |fB/fX| = 3.639

FIGS. 2A, 2B and 2C show aberrations of the zoom optical systemaccording to the first example in the state in which the optical systemis focused on an object point at infinity, where FIG. 2A showsaberrations at the wide angle end of the focal length range, FIG. 2Bshows aberrations at the intermediate focal length position, and FIG. 2Cshows aberrations at the telephoto end of the focal length range.

FIGS. 3A and 3B show aberrations of the zoom optical system according tothe first example in the state in which the optical system is focused onan object point at a short distance, where FIG. 3A shows aberrations atthe wide angle end of the focal length range, and FIG. 3B showsaberrations at the telephoto end of the focal length range.

In the aberration diagrams, FNO is the F-number FNO, Y is the imageheight Y, and NA is the numerical aperture. Curves d representaberrations with respect to the d-line (having a wavelength of 587.6nm), curves g represent aberrations with respect to the g-line (having awavelength of 435.8 nm), and curves with no denotation also representaberrations with respect to the d-line. In the diagrams of astigmatism,the solid lines represent the sagittal image surface and the brokenlines represent the meridional image surface.

Like symbols will also be used in the examples described in thefollowing to eliminate redundant description.

From the aberration diagrams, it can be seen that aberrations of thezoom optical system according to the first example are excellentlycorrected throughout the focal length range from the wide angle end tothe telephoto end, and excellent optical performance is achieved.

Second Example

FIG. 4 is a cross sectional view showing the configuration of a zoomoptical system according to a second example.

As shown in FIG. 4, the zoom optical system according to the secondexample includes, in order from its object side along its optical axis,a first lens group G1 having a positive refracting power, a second lensgroup G2 having a negative refracting power, a third lens group G3having a positive refracting power, and a fourth lens group G4 having apositive refracting power. The third lens group G3 is composed of afront group G3A having a positive refracting power and a rear group G3Bhaving a negative refracting power. An aperture stop S is provided inthe fourth lens group G4, and the aperture stop S is the element that islocated closest to the object side in the fourth lens group G4.

During zooming from the wide angle end state W to the telephoto endstate T, the first lens group G1 is fixed, the second lens group G2moves monotonically toward the image side, the third lens group G3moves, and the fourth lens group G4 is fixed, relative to the imageplane I so that the distance between the first lens group G1 and thesecond lens group G2 increases, that the distance between the secondlens group G2 and the third lens group G3 changes, and that the distancebetween the third lens group G3 and the fourth lens group G4 changes. Inaddition, during zooming from the wide angle end state W to thetelephoto end state T, the distance between the front group G3A in thethird lens group G3 and the rear group G3B in the third lens group G3does not change.

Focusing operation from an object at infinity to an object at a shortdistance is performed by moving the front group G3A in the third lensgroup G3 toward the image side along the optical axis.

The first lens group G1 includes, in order from the object side alongthe optical axis, a cemented lens made up of a negative meniscus lensL11 having a convex surface facing the object side and a biconvex lensL12, and a positive meniscus lens L13 having a convex surface facing theobject side.

The second lens group G2 includes, in order from the object side alongthe optical axis, a biconcave lens L21, a cemented lens made up of abiconcave lens L22 and a biconvex lens L23, and a biconcave lens L24.The front group G3A in the third lens group G3 includes a cemented lensmade up of a negative meniscus lens L31 having a convex surface facingthe object side and a biconvex lens L32, which are arranged in orderfrom the object side along the optical axis.

The rear group G3B in the third lens group G3 includes a cemented lensmade up of a positive meniscus lens L33 having a concave surface facingthe object side and a negative meniscus lens L34 having a concavesurface facing the object side, which are arranged in order from theobject side along the optical axis.

The fourth lens group G4 includes, in order from the object side alongthe optical axis, a biconvex lens L41, a cemented lens made up of abiconvex lens L42 and a biconcave lens L43, a first fixed stop FS1, acemented lens made up of a biconvex lens L44 and a biconcave lens L45, abiconcave lens L46, a second fixed stop FS2, a biconvex lens L47, abiconvex lens L48, and a negative meniscus lens L49 having a concavesurface facing the object side. The rays emerging from the negativemeniscus lens L49 are focused on the image plane I.

Hand-shake compensation (or vibration reduction) is provided by moving aportion of the fourth lens group G4 or the cemented lens made up of thebiconvex lens L44 and the biconcave lens L45 and the biconcave lens L46in such a way as to have a movement component in a directionperpendicular to the optical axis.

Numerical data for the zoom optical system according to the secondexample is presented in Table 2 below.

TABLE 2 (Surface Data) SN r d nd νd OP ∞ ∞  1 119.0272 2.5000 1.85023932.28  2 68.7833 8.8000 1.497820 82.52  3 −1818.7811 0.1000  4 64.30558.5000 1.497820 82.52  5 11508.8650 (variable)  6 −379.9571 2.00001.834686 41.78  7 41.3382 5.2354  8 −83.4183 1.8000 1.496012 70.17  941.6721 4.8071 1.846660 23.78 10 −256.8116 1.7266 11 −64.7335 1.80001.816000 46.62 12 299.1015 (variable) 13 83.7734 2.0000 1.834000 37.1614 37.7766 6.6162 1.667767 57.98 15 −74.3595 (variable) 16 −41.16042.5000 1.774638 33.11 17 −32.5471 2.0000 1.688932 30.87 18 −54.8952(variable) 19 (stop) ∞ 0.0000 20 45.9764 4.6261 1.718637 51.17 21−165.7976 0.1000 22 31.4873 4.5489 1.497820 82.52 23 −151.4615 2.00001.850260 32.35 24 34.3531 14.2150  25 ∞ 2.0000 26 98.7847 3.61161.775455 23.76 27 −36.5164 1.6000 1.696797 55.52 28 57.3439 2.5204 29−222.2566 1.6000 1.841287 29.70 30 45.4216 1.7957 31 ∞ 1.5000 32 55.95233.9000 1.512753 64.87 33 −95.7605 0.1000 34 70.3942 3.9000 1.51236764.95 35 −128.2012 5.0000 36 −32.2481 1.9000 1.800999 34.96 37 −48.1025(Bf) IP ∞ W M T (various data) Zoom ratio: 2.746 f = 71.40 107.00 196.00FNO = 4.2 4.2 4.2 ω = 17.230 11.311 6.089 Y = 21.6 21.6 21.6 TL = 214.8214.6 214.7 Bf = 52.8 52.6 52.7 d5 1.840 20.803 38.591 d12 25.924 19.0841.135 d15 16.066 16.066 16.066 d18 12.762 0.638 0.800 (Data for ShortObject Distance) β −0.04 −0.05 −0.09 d0 1785.25 1785.43 1785.36 d5 1.84020.803 38.591 d12 27.329 22.044 10.057 d15 14.660 13.106 7.144 d1812.762 0.638 0.800 (Data for Zoom Lens Group) Group FLS FL 1 1 101.340 26 −29.089 3 13 86.501 3A 13 69.999 3B 16 −333.927 4 19 99.569 (valuesAssociated with Conditions) (1) |fA/fB| = 0.210 (2) |fA/fX| = 0.809 (3)|fB/fX| = 3.860

FIGS. 5A, 5B and 5C show aberrations of the zoom optical systemaccording to the second example in the state in which the optical systemis focused on an object point at infinity, where FIG. 5A showsaberrations at the wide angle end of the focal length range, FIG. 5Bshows aberrations at the intermediate focal length position, and FIG. 5Cshows aberrations at the telephoto end of the focal length range.

FIGS. 6A and 6B show aberrations of the zoom optical system according tothe second example in the state in which the optical system is focusedon an object point at a short distance, where FIG. 6A shows aberrationsat the wide angle end of the focal length range, and FIG. 6B showsaberrations at the telephoto end of the focal length range.

From the aberration diagrams, it can be seen that aberrations of thezoom optical system according to the first example are excellentlycorrected throughout the focal length range from the wide angle end tothe telephoto end, and excellent optical performance is achieved.

Third Example

FIG. 7 is a cross sectional view showing the configuration of a zoomoptical system according to a third example.

As shown in FIG. 7, the zoom optical system according to the thirdexample includes, in order from its object side along its optical axis,a first lens group G1 having a positive refracting power, a second lensgroup G2 having a negative refracting power, a third lens group G3having a positive refracting power, and a fourth lens group G4 having apositive refracting power. The first lens group G1 is composed of afront group G1A having a positive refracting power and a rear group G1Bhaving a negative refracting power. An aperture stop S is provided inthe fourth lens group G4, and the aperture stop S is the element that islocated closest to the object side in the fourth lens group G4.

During zooming from the wide angle end state W to the telephoto endstate T, the first lens group G1 is fixed, the second lens group G2moves monotonically toward the image side, the third lens group G3moves, and the fourth lens group G4 is fixed, relative to the imageplane I so that the distance between the first lens group G1 and thesecond lens group G2 increases, that the distance between the secondlens group G2 and the third lens group G3 changes, and that the distancebetween the third lens group G3 and the fourth lens group G4 changes. Inaddition, during zooming from the wide angle end state W to thetelephoto end state T, the distance between the front group G1A in thefirst lens group G1 and the rear group G1B in the first lens group G1does not change.

Focusing operation from an object at infinity to an object at a shortdistance is performed by moving the front group G1A in the first lensgroup G1 toward the object side along the optical axis.

The front group G1A in the first lens group G1 includes, in order fromthe object side along the optical axis, a positive meniscus lens L11having a convex surface facing the object side, a cemented lens made upof a negative meniscus lens L12 having a convex surface facing theobject side and a biconvex lens L13, and a positive meniscus lens L14having a convex surface facing the object side.

The rear group G1B in the first lens group G1 includes a negativemeniscus lens L15 having a convex surface facing the object side.

The second lens group G2 includes, in order from the object side alongthe optical axis, a biconcave lens L21, a cemented lens made up of abiconcave lens L22 and a biconvex lens L23, and a biconcave lens L24.The biconcave lens L21 is a glass mold aspheric lens having an asphericimage side lens surface.

The third lens group G3 includes a cemented lens made up of a biconvexlens L31 and a negative meniscus lens L32 having a concave surfacefacing the object side, which are arranged in order from the object sidealong the optical axis.

The fourth lens group G4 includes, in order from the object side alongthe optical axis, a positive meniscus lens L41 having a convex surfacefacing the object side, a cemented lens made up of a biconvex lens L42and a biconcave lens L43, a first fixed stop FS1, a cemented lens madeup of a biconvex lens L44 and a biconcave lens L45, a biconcave lensL46, a second fixed stop FS2, a biconvex lens L47, a biconvex lens L48,and a negative meniscus lens L49 having a concave surface facing theobject side. The rays emerging from the negative meniscus lens L49 arefocused on the image plane I.

Hand-shake compensation (or vibration reduction) is provided by moving aportion of the fourth lens group G4 or the cemented lens made up of thebiconvex lens L44 and the biconcave lens L45 and the biconcave lens L46in such a way as to have a movement component in a directionperpendicular to the optical axis.

Numerical data for the zoom optical system according to the thirdexample is presented in Table 3 below.

TABLE 3 (Surface Data) SN r d nd νd OP ∞ ∞  1 166.2990 3.1000 1.48749070.40  2 875.3645 1.5000  3 152.4026 2.0000 1.903660 31.27  4 83.27965.9000 1.497820 82.52  5 −295.6182 0.1000  6 67.8904 5.0000 1.49782082.52  7 445.0552 (variable)  8 252.9956 2.0000 1.638731 56.93  9140.7312 (variable) 10 −1759.9066 1.4500 1.820800 42.60 11* 42.25754.0493 12 −69.0136 1.2500 1.603001 65.46 13 40.1840 3.8171 1.84666023.78 14 −276.1554 1.1764 15 −62.0184 1.2500 1.772499 49.61 16 469.7053(variable) 17 281.3799 5.5016 1.719995 50.23 18 −32.3692 1.4000 1.90366031.27 19 −66.3391 (variable) 20 (stop) ∞ 0.4000 21 50.0344 5.00001.804000 46.57 22 3065.4479 0.3000 23 34.9606 5.5000 1.497820 82.52 24−144.0312 1.9970 1.903660 31.27 25 40.4149 14.5500  26 ∞ 2.4000 2797.9375 4.1737 1.805181 25.43 28 −42.1393 1.2000 1.603112 60.67 2967.8195 4.0000 30 −198.3164 1.2000 2.000690 25.45 31 62.5639 0.9000 32 ∞2.0016 33 84.5408 4.6000 1.589130 61.16 34 −84.5408 0.7000 35 71.04755.0000 1.712995 53.88 36 −71.0472 5.7414 37 −42.5291 2.0400 1.83400037.16 38 −165.3314 (Bf) IP ∞ (Aspheric Surface Data) 11th surface κ =1.4043 A4 = −5.20200E−07 A6 = −5.33060E−10 W M T (Various Data) Zoomratio: 2.745 f = 71.40 103.00 196.00 FNO = 4.1 4.1 4.1 ω = 17.233 11.7346.106 Y = 21.6 21.6 21.6 TL = 209.8 209.8 209.8 Bf = 64.0 64.0 64.0 d71.500 1.500 1.500 d9 1.950 19.263 39.917 d16 20.437 16.356 1.200 d1920.686 7.426 1.900 (Data for Short Object Distance) β −0.06 −0.09 −0.16d0 1273.46 1273.49 1273.52 d7 8.211 8.211 8.211 d9 1.950 19.263 39.917d16 20.437 16.356 1.200 d19 20.686 7.426 1.900 (Data for Zoom LensGroup) Group FLS FL 1 1 106.4334 1A 1 89.655 1B 8 −500.000 2 10 −28.0093 17 95.490 4 20 81.135 (Values Associated with Conditions) (1) |fA/fB|= 0.179 (2) |fA/fX| = 0.842 (3) |fB/fX| = 4.698

FIGS. 8A, 8B and 8C show aberrations of the zoom optical systemaccording to the third example in the state in which the optical systemis focused on an object point at infinity, where FIG. 8A showsaberrations at the wide angle end of the focal length range, FIG. 8Bshows aberrations at the intermediate focal length position, and FIG. 8Cshows aberrations at the telephoto end of the focal length range.

FIGS. 9A and 9B show aberrations of the zoom optical system according tothe third example in the state in which the optical system is focused onan object point at a short distance, where FIG. 9A shows aberrations atthe wide angle end of the focal length range, and FIG. 9B showsaberrations at the telephoto end of the focal length range.

From the aberration diagrams, it can be seen that aberrations of thezoom optical system according to the third example are excellentlycorrected throughout the focal length range from the wide angle end tothe telephoto end, and excellent optical performance is achieved.

Fourth Example

FIG. 10 is a cross sectional view showing the configuration of a zoomoptical system according to a fourth example.

As shown in FIG. 10, the zoom optical system according to the fourthexample includes, in order from its object side along its optical axis,a first lens group G1 having a positive refracting power, a second lensgroup G2 having a negative refracting power, a third lens group G3having a positive refracting power, a fourth lens group G4 having apositive refracting power, and a fifth lens group G5 having a negativerefracting power. The third lens group G3 is composed of a front groupG3A having a positive refracting power and a rear group G3B having anegative refracting power. An aperture stop S is provided in the fourthlens group G4, and the aperture stop S is the element that is locatedclosest to the object side in the fourth lens group G4.

During zooming from the wide angle end state W to the telephoto endstate T, the first lens group G1 is fixed, the second lens group G2moves monotonically toward the image side, the third lens group G3moves, the fourth lens group G4 moves monotonically toward the objectside, and the fifth lens group G5 is fixed, relative to the image planeI so that the distance between the first lens group G1 and the secondlens group G2 increases, that the distance between the second lens groupG2 and the third lens group G3 changes, that the distance between thethird lens group G3 and the fourth lens group G4 changes, and that thedistance between the fourth lens group G4 and the fifth lens group G5changes. In addition, during zooming from the wide angle end state W tothe telephoto end state T, the distance between the front group G3A inthe third lens group G3 and the rear group G3B in the third lens groupG3 does not change.

Focusing operation from an object at infinity to an object at a shortdistance is performed by moving the front group G3A in the third lensgroup G3 toward the image side along the optical axis.

The first lens group G1 includes, in order from the object side alongthe optical axis, a cemented lens made up of a negative meniscus lensL11 having a convex surface facing the object side and a biconvex lensL12, and a positive meniscus lens L13 having a convex surface facing theobject side.

The second lens group G2 includes, in order from the object side alongthe optical axis, a negative meniscus lens L21 having a convex surfacefacing the object side, a cemented lens made up of a biconcave lens L22and a biconvex lens L23, and a biconcave lens L24.

The front group G3A in the third lens group G3 includes, in order fromthe object side along the optical axis, a biconvex lens L31, and acemented lens made up of a negative meniscus lens L32 having a convexsurface facing the object side and a biconvex lens L33.

The rear group G3B in the third lens group G3 includes a negativemeniscus lens L34 having a concave surface facing the object side.

The fourth lens group G4 includes, in order from the object side alongthe optical axis, a biconvex lens L41, and a cemented lens made up of abiconvex lens L42 and a biconcave lens L43.

The fifth lens group G5 includes, in order from the object side alongthe optical axis, a first fixed stop FS1, a cemented lens made up of abiconvex lens L51 and a biconcave lens L52, a biconcave lens L53, asecond fixed stop FS2, a biconvex lens L54, a biconvex lens L55, and anegative meniscus lens L56 having a concave surface facing the objectside. The rays emerging from the negative meniscus lens L56 are focusedon the image plane I.

Hand-shake compensation (or vibration reduction) is provided by moving aportion of the fifth lens group G5 or the cemented lens made up of thebiconvex lens L51 and the biconcave lens L52 and the biconcave lens L53in such a way as to have a movement component in a directionperpendicular to the optical axis.

Numerical data for the zoom optical system according to the fourthexample is presented in Table 4 below.

TABLE 4 (Surface Data) SN r d nd νd OP ∞ ∞  1 105.5853 2.5000 1.83079033.24  2 61.8846 8.8000 1.497820 82.52  3 −2502.4443 0.1000  4 61.04858.5000 1.497820 82.52  5 3247.1190 (variable)  6 1271.6072 2.00001.812260 39.72  7 32.2961 6.6220  8 −72.5848 1.8000 1.487588 70.50  936.7994 5.0132 1.846586 23.78 10 −408.4276 2.4231 11 −51.3707 1.80001.729273 54.64 12 460.3188 (variable) 13 133.8896 3.2225 1.729405 54.6314 −138.3727 0.1000 15 123.3360 2.0000 1.834000 37.16 16 39.9361 5.90001.603001 65.46 17 −99.2430 (variable) 18 −50.0000 2.0000 1.755199 27.5119 −69.2551 (variable) 20 (stop) ∞ 0.1000 21 53.4321 3.7929 1.71631555.44 22 −237.0413 0.1000 23 41.6389 4.0000 1.497820 82.52 24 −6903.86892.0000 1.849124 31.49 25 44.4196 (variable) 26 ∞ 2.0000 27 71.73923.4000 1.808090 22.79 28 −105.2565 1.6000 1.692515 55.47 29 34.49412.6264 30 −771.7031 1.6000 1.840743 30.47 31 64.2379 1.5000 32 ∞ 1.500033 47.7790 4.1209 1.514290 65.99 34 −96.1820 0.1000 35 62.0757 3.90001.504175 66.58 36 −311.1825 4.4088 37 −33.3826 1.9000 1.800999 34.96 38−53.0369 (Bf) IP ∞ (Various Data) Zoom ratio: 2.750 W M T f = 71.23106.79 195.89 FNO = 4.25 4.25 4.25 ω = 17.157 11.303 6.110 Y = 21.6 21.621.6 TL = 214.5 214.5 214.5 Bf = 51.8 51.8 51.8 d5 1.500 17.629 33.797d12 22.173 15.365 0.807 d17 13.158 13.158 13.158 d19 17.641 5.443 0.700d25 16.778 19.655 22.778 (Data for Short Object Distance) β −0.08 −0.11−0.17 d0 775.71 775.71 775.71 d5 1.500 17.629 33.797 d12 24.729 20.09112.703 d17 10.603 8.433 1.273 d19 17.641 5.443 0.700 d25 16.778 19.65522.778 (Data for Zoom Lens Group) Group FLS FL 1 1 94.857 2 6 −25.937 313 69.658 3A 13 57.563 3B 18 −249.271 4 20 88.043 5 26 −412.603 (ValuesAssociated with Conditions) (1) |fA/fB| = 0.231 (2) |fA/fX| = 0.826 (3)|fB/fX| = 3.579

FIGS. 11A, 11B and 11C show aberrations of the zoom optical systemaccording to the fourth example in the state in which the optical systemis focused on an object point at infinity, where FIG. 11A showsaberrations at the wide angle end of the focal length range, FIG. 11Bshows aberrations at the intermediate focal length position, and FIG.11C shows aberrations at the telephoto end of the focal length range.

FIGS. 12A and 12B show aberrations of the zoom optical system accordingto the fourth example in the state in which the optical system isfocused on an object point at a short distance, where FIG. 12A showsaberrations at the wide angle end of the focal length range, and FIG.12B shows aberrations at the telephoto end of the focal length range.

From the aberration diagrams, it can be seen that aberrations of thezoom optical system according to the fourth example are excellentlycorrected throughout the focal length range from the wide angle end tothe telephoto end, and excellent optical performance is achieved.

As described above, zoom optical systems having good optical performancecan be provided according to the present embodiment.

A camera equipped with a zoom optical system according to the presentembodiment will be described. In the following, a camera equipped withthe zoom optical system according to the first example will bedescribed. The following description also applies to a camera equippedwith the zoom optical system according to any one of the other examples.

FIG. 13 is a cross sectional view schematically showing the constructionof a camera equipped with the zoom optical system according to the firstexample.

FIG. 13 shows a digital single lens reflex camera 1 equipped with thezoom optical system according to the first example as the taking lens 2.In this camera 1, light coming from an object (not shown) is condensedby the taking lens 2 and focused on a focusing screen 4 through aquick-return mirror 3. The light focused on the focusing screen 4 isguided to an eyepiece lens 6 after reflected plural times in apentaprism 5. Thus, a user or photographer can see an erected image ofthe object through the eyepiece lens 6.

As a shutter release button (not shown) is depressed by thephotographer, the quick-return mirror 3 is removed out of the opticalpath to allow light from the object (not shown) to reach an image pickupelement 7. Thus, light from the object is picked up by the image pickupelement 7 and recorded as an object image in a memory (not shown). Thephotographer takes an image of an object with the camera 1 in this way.

With the use of the zoom optical system according to the first exampleas the taking lens 2 of the camera 1, the camera 1 can have high opticalperformance.

In the following, a method of manufacturing a zoom optical systemaccording to the present application will be described.

FIG. 14 is a flow chart of the method of manufacturing the zoom opticalsystem according to the present application.

The method of manufacturing a zoom optical system according to thepresent invention is a method of manufacturing a zoom optical systemincluding, in order from the object side along the optical axis, a firstlens group having a positive refracting power, a second lens grouphaving a negative refracting power, a third lens group having a positiverefracting power, and a fourth lens group having a positive refractingpower. The method comprises steps S1, S2 and S3 shown in FIG. 14.

Step S1: Constructing at least one of the first, second, third andfourth lens groups with a front group having a positive refracting powerincluding at least two lenses and a rear group having a negativerefracting power.

Step S2: Arranging the front group and the rear group in such a way thatthe distance between the front group and the rear group will not changeduring zooming from the wide angle end state to the telephoto end state.

Step 3: Arranging the front group in such a way as to be movable alongthe optical axis upon focusing onto an object.

With the method of manufacturing a zoom optical system according to thepresent invention, a zoom optical system having good optical performancecan be manufactured.

One or more of the following features may be adopted as long as theoptical performance of the zoom optical system is not deteriorated.

Although the optical systems according to the present application have afour-group configuration or five-group configuration, the presentinvention can also be applied to optical systems having other lens groupconfigurations such as six-group configuration. Alternatively, a lens orlens group may be added to the optical system as the lens or the lensgroup located closest to the object side, or as the lens or the lensgroup located closest to the image side. The term “lens group” refers toa unit that includes at least one lens and is separated from anotherunit by an air gap that changes during zooming.

One or plurality of lens groups or a partial lens group may serve as afocusing lens group(s) that is moved along the optical axis for focusingfrom an object at infinity to an object at a short distance. Thefocusing lens group may also be used in an auto-focus optical systemsuitably with motor driving (using, for example, an ultrasonic motor)for auto-focusing. In particular it is preferred that the first or thirdlens group serve as the focusing lens group.

One lens group or partial lens group may serve as a vibration reductionlens group that is moved in such a way as to have a movement componentin a direction perpendicular to the optical axis or moved rotationally(or swung) in a direction in a plane containing the optical axis toreduce image blur caused by hand shake. In particular it is preferredthat at least a part of the fourth lens group serve as the vibrationreduction lens group.

The lens surfaces may be spherical, planar, or aspheric.

Spherical or planar lens surfaces are preferred in facilitatingmachining, assembly and adjustment and preventing deterioration in theoptical performance caused by errors in machining, assembly andadjustment. In addition, they are preferred because even when the imageplane is displaced, a large deterioration in the image quality is notcaused if the lens surfaces are spherical or planar.

Aspheric surfaces, if any, may be produced by grinding. Alternatively,they may be glass mold aspheric surfaces produced by shaping glass witha mold or composite aspheric surfaces produced by molding resin on aglass surface. The lens surfaces may be diffractive surfaces. Gradientindex lenses (GRIN lenses) and plastic lenses may also be used.

It is preferred that the aperture stop be disposed near the fourth lensgroup. Alternatively, a lens frame may be adapted to serve as anaperture stop to eliminate a separate aperture stop.

Anti-reflection coating achieving high transmittance over a widewavelength range may be applied to the lens surfaces to achieveexcellent optical performance with high contrast and reduced lens flaresand ghost images.

The zoom optical systems according to the embodiment have a zoom ratiowithin a range of approximately 2 to 5.

In the zoom optical systems according to the embodiment, it is preferredthat the first lens group include two positive lens components.

In the zoom optical systems according to the embodiment, it is preferredthat the second lens group include three negative lens components.

In the zoom optical systems according to the embodiments, it ispreferred that the third lens group include one positive lens component.

In the zoom optical systems according to the embodiments, it ispreferred that the fourth lens group include one positive lens componentand one negative lens component.

In the zoom optical systems according to the embodiment, it is preferredthat the fifth lens group include one positive lens component and onenegative lens component.

Although various components of the embodiment have been described tofacilitate understanding of the present invention, the present inventionis not limited to them.

1. A zoom optical system comprising, in order from its object side alongits optical axis: a first lens group having a positive refracting power;a second lens group having a negative refracting power; a third lensgroup having a positive refracting power; and a fourth lens group havinga positive refracting power, wherein at least one of said first, second,third and fourth lens groups comprises a front group having a positiverefracting power including at least two lenses and a rear group having anegative refracting power, and during zooming from the wide angle endstate to the telephoto end state, the distance between said front groupand said rear group does not change, and during focusing onto an object,said front lens group moves along the optical axis.
 2. A zoom opticalsystem according to claim 1, wherein said first lens group is fixedrelative to an image plane during zooming from the wide angle end stateto the telephoto end state.
 3. A zoom optical system according to claim1, wherein the zoom optical system satisfies the following condition:0.050<|fA/fB|<0.950, where fA is the focal length of said front group,and fX is the focal length of said rear group.
 4. A zoom optical systemaccording to claim 1, wherein the lens group located closest to theimage side is fixed relative to an image plane during zooming from thewide angle end state to the telephoto end state.
 5. A zoom opticalsystem according to claim 1, at least a part of said fourth lens groupis movable with a movement component in a direction perpendicular to theoptical axis.
 6. A zoom optical system according to claim 1, wherein thezoom optical system satisfies the following condition:0.050<|fA/fX|<0.950, where fA is the focal length of said front group,and fX is the focal length of said at least one lens group.
 7. A zoomoptical system according to claim 1, wherein the zoom optical systemsatisfies the following condition:1.200<|fB/fX|<50.000, where fB is the focal length of said rear group,and fX is the focal length of said at least one lens group.
 8. A zoomoptical system according to claim 1, wherein the lens group includingsaid front group and said rear group is said third lens group.
 9. A zoomoptical system according to claim 1, wherein the lens group includingsaid front group and said rear group is said first lens group.
 10. Azoom optical system according to claim 1, wherein said front groupcomprises at least one positive lens and at least one negative lens. 11.A zoom optical system according to claim 1, wherein during zooming fromthe wide angle end state to the telephoto end state, the distancebetween said first lens group and said second lens group increases, thedistance between said second lens group and said third lens groupchanges, and the distance between said third lens group and said fourthlens group changes.
 12. An optical apparatus having a zoom opticalsystem according to claim
 1. 13. A method of manufacturing a zoomoptical system including, in order from its object side along itsoptical axis, a first lens group having a positive refracting power, asecond lens group having a negative refracting power, a third lens grouphaving a positive refracting power and a fourth lens group having apositive refracting power, the method comprising: constructing at leastone of said first, second, third and fourth lens groups with a frontgroup having a positive refracting power including at least two lensesand a rear group having a negative refracting power; arranging saidfront group and said rear group in such a way that the distance betweensaid front group and said rear group will not change during zooming fromthe wide angle end state to the telephoto end state; and arranging saidfront group in such a way as to be movable along the optical axis uponfocusing onto an object.
 14. A method of manufacturing a zoom opticalsystem according to claim 13, further comprising a step of arrangingsaid first lens group in such a way to be fixed relative to an imageplane during zooming from the wide angle end state to the telephoto endstate.
 15. A method of manufacturing a zoom optical system according toclaim 13, wherein the zoom optical system satisfies the followingcondition:0.050<|fA/fB|<0.950, where fA is the focal length of said front group,and fX is the focal length of said rear group.
 16. A method ofmanufacturing a zoom optical system according to claim 13, wherein thezoom optical system satisfies the following condition:0.050<|fA/fX|<0.950, where fA is the focal length of said front group,and fX is the focal length of said at least one lens group.
 17. A methodof manufacturing a zoom optical system according to claim 13, whereinthe zoom optical system satisfies the following condition:1.200<|fB/fX|<50.000, where fB is the focal length of said rear group,and fX is the focal length of said at least one lens group.